Rotary control valve for screw compressors

ABSTRACT

A liquid injected helical screw gas compressor having a capacity control valve comprising a cylindrical plug member fitted in a chamber which is adjacent to and in communication with the compressor working chambers by way of a series of auxiliary ports. The control valve member includes a control edge coacting with the auxiliary ports for controlling the gas throughput and the built-in volume ratio of the compressor. The control valve member also includes a series of liquid injection passages spaced along and around the perimeter of the cylindrical plug. The liquid injection passages are selectively placed in communication with the auxiliary ports in accordance with the control valve position for controlling the position and rate of injection of liquid into the working chambers.

United States Patent [1 1 Herschler et al.

[ Apr. 1,1975

[ ROTARY CONTROL VALVE FOR SCREW CQMPRESSORS [73] Assignee:Gardner-Denver Company, Quincy,

[22] Filed: Nov. 12, 1973 [21] Appl. No.: 415,279

[52] US. Cl 418/87, 418/97, 418/201 [51] Int. Cl...... F0lc 21/04, F04029/02, F01c 1/16 [58] Field of Search 418/87, 97, 159, 20l203;

3,432,089 3/1969 Schibbye 418/201 FOREIGN PATENTS OR APPLICATIONS UnitedKingdom 418/97 Primary E.\'aminer.lohn .1. Vt'ablik Attorney, Agent, orFirm-M. E. Martin [5 7] ABSTRACT A liquid injected helical screw gascompressor having a capacity control valve comprising a cylindrical plugmember fitted in a chamber which is adjacent to and in communicationwith the compressor working chambers by way of a series of auxiliaryports. The control valve member includes a control edge coating with theauxiliary ports for controlling the gas throughput and the built-involume ratio of the compressor. The control valve member also includes aseries of liquid injection passages spaced along and around theperimeter of the cylindrical plug. The liquid injection passages areselectively placed in communication with the auxiliary ports inaccordance with the control valve position for controlling the positionand rate of injection of liquid into the working chambers,

11 Claims, 15 Drawing Figures PATENTED APR 1 i975 SHEET 1 7 ROTARYCONTROL VALVE FOR SCREW COMPRESSORS BACKGROUND OF THE INVENTION In theart of helical screw rotor compressors it has been suggested to providefor control of the gas throughput of the machine and the built-in volumeratio by opening and closing auxiliary ports in the bore walls of theworking chambers in which the cooperating screw rotors are disposed.U.S. Pat. No. 3,088,658 to H. B. Wagenius discloses a rotary regulatingvalve device which is disposed in a cylindrical chamber adjacent to thescrew rotor bores. A control edge on the rotary valve membersequentially uncovers a series of auxiliary ports for bypassing back tothe compressor inlet port certain portions of the compressor workingfluid entrapped in the rotor grooves. Other forms of capacity controldevices have been suggested including the axial slide valve devicesdisclosed in US. Pat. Nos. 3,088,659 and 3,314,597. Generally, thearrangement including the rotary type capacity control valve has beenfound to be more economical to manufacture and does not require theprecision with which the axial slide valve must be supported in thecompressor casing.

The rotary regulating or capacity control valve has generally not provento be as suitable as the axial slide valve when considering the overalloperating efficiency of certain types of helical screw rotor machinesbecause of the unavoidable unswept volume formed by the auxiliary portswhich open into the compressor working chambers. However, in accordancewith the present invention this problem has been substantially overcomeby the use of the rotary capacity control valve in a helical screw gascompressor in which liquid is injected directly into the compressorworking chambers. Moreover, improvements realized with the presentinvention concerning the amount of liquid injected and the location ofthe injection passages with respect to the working chambers have alsocontributed measurably to improving the efficiency of compressors of thesubject type.

SUMMARY OF THE INVENTION The present invention provides for an improvedliquid injected helical screw rotor gas compressor which includes arotary capacity control valve characterized by a cylindrical plug memberhaving a control edge which coacts with a series of ports in the workingchambers to effect the sequential opening and closing of said ports toregulate the gas throughput and built-in volume ratio of the compressor.With the use of a rotary capacity control valve in a helical screw gascompressor in accordance with the present invention improvements incompressor operating efficiency have been realized thereby overcomingthe disadvantages which previously burdened helical screw rotor machineswith rotary type capacity regulating devices.

Further, in accordance with the present invention, a rotary capacitycontrol valve is provided in a helical screw gas compressor which iscapable of regulating the amount of liquid injected into the compressorworking chambers as well as the location of the liquid injectionpassagesin accordance with the rotative position of the valve memberitself. In this way the desired flow rate of liquid and the location ofinjection into the compressor working chambers can be convenientlycontrolled in accordance with the gas throughput and the workingpressure of the compressor.

The present invention also provides a liquid injected gas compressorwhich includes a structurally simple and reliable capacity controldevice which may be provided in a form for use with compressors whereonly infrequent adjustment of compressor capacity is required.Accordingly, with the present invention a capacity controlled liquidinjected gas compressor is realized which is not only economical tomanufacture but is more efficient than certain prior art screwcompressors with attendant capacity regulating devices.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal section viewof a helical screw compressor in accordance with the present inventionand is taken along line l1 of FIG. 4;

FIG. 2 is a schematic view of a liquid injected compressor systemincluding the compressor of FIG. 1;

FIG. 3 is a section view taken along line 3-3 of FIG.

FIG. 4 is a section view taken along line 4--4 of FIG.

FIG. 5 is a section view taken along line 55 of FIG.

FIG. 6 is a perspective view of the control valve member of thecompressor of FIG. 1;

FIGS. 7 through 10 are planar developments of the cylindrical controlvalve chamber of the compressor of FIG. 1 and illustrating the auxiliaryports and various angular positions of the control edge and liquidinjection passages of the control valve member;

FIG. 11 is a longitudinal section view of a second embodiment of aliquid injected helical screw gas compressor in accordance with thepresent invention and is taken along line l111 of FIG. 12;

FIG. 12 is a transverse section taken along line l212 of FIG. 11;

FIG. 13 is a perspective view of the control valve member of thecompressor of FIG. 11;

FIG. 14 is a planar development of the cylindrical surface of thecontrol valve member of the compressor of FIG. 11 illustrating theauxiliary ports and two positions of the control valve member; and,

FIG. 15 is a view taken from the line 15l5 of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 4 ofthe drawings, a liquid injected helical screw gas compressor inaccordance with the present invention is generally designated by thenumeral 10. The compressor 10 includes a main casing 12 having parallelintersecting bores 14 and 16, a bearing support member 18 forming an endwall 20, and a bearing support member 22 forming an end wall 24. Thebores 14 and 16 form working chambers together with a pair ofcooperating main and gate helical screw rotors 26 and 28. The gate rotor28 is provided with six helical lobes 30 and intervening grooves 32 andincludes oppositely projecting shaft end portions which are supported inbearings 34 and 36. The main rotor 26 is provided with four helicallobes 38 and intervening grooves 40 and is similarly supported bybearings, not shown, disposed in the housing members 18 and 22. The mainrotor 26 also includes a shaft portion 42 which extends from an endcover 44 for connecting the compressor to a rotary power source such asa motor, turbine, internal combustion engine or the like. In a known waythe rotors 26 and 28 cooperate with each other and with the casing 12and end walls and 24 for compressing fluid trapped in the grooves 32 and40 as the rotors rotate together. In the compressor 10 the main rotor 26drivingly engages the gate rotor 28 although synchronizing gears can beused to form the driving engagement between the rotors as is known inthe art of helical screw rotor machines. The lobes and grooves of themain rotor 26 have a wrap angle of about 300 and the lobes and groovesof the gate rotor 28 have a wrap angle of about 200. Other combinationsof lobes and wrap angles may be used with the advantageous features ofthe present invention.

The casing 12 includes an opening 46 which is in communication with alow pressure or inlet port 48 formed in the casing and partly in themember 22 whereby gas may be admitted to the bores 14 and 16 forcompression by the rotors 26 and 28. The compressor 10 also includes ahigh pressure or discharge port 50 formed substantially in the end wall20 and also having a portion 52 disposed in the casing 12. Gascompressed by the intermeshing rotors 26 and 28 is discharged throughthe port 50 and into a passage 54 in a substantially continuous andpulsation free flow when the compressor 10 is in operation.

The compressor 10 is suitably adapted for the injection of liquid intothe bores 14 and 16, as will be explained in greater detail herein, forsealing the spaces, formed between the rotors 26 and 28 and the walls ofthe bores 14 and 16 as well as the end walls 20 and 24. The liquidinjected into the working chambers formed in the bores 14 and 16 alsoabsorbs at least part of the heat of compression of the gas beingcompressed and is pumped through the discharge port 50 with thecompressed gas to be separated therefrom by suitable means downstream ofthe compressor proper. The injection liquid is preferably an oil whichis also used as a lubricant for the intermeshed rotors and the bearingsof the compressor.

As shown in FIGS. 1, 4, and 5 the casing 12 also includes an elongatedcylindrical chamber 56 formed adjacent and substantially parallel to thebores 14 and 16. The casing 12 further includes passages. 58 and 60which are in communication with the chamber 56 and with the inlet port48 formed in the casing. The chamber 56 is in'communication with thebores 14 and 16 by a series of auxiliary ports 62 opening into the bore16 and a series of auxiliary ports 64 which open into the bore 14. Theconfiguration and relative positions of the auxiliary ports 62 and 64are more clearly shown by the planar developments of the bore wall ofthe cylindrical chamber 56 shown in FIGS. 7 through 10. The ports 62 and64 are generally formed as spaced apart oblique slots disposed along andon each side of the line of intersection of the bores 14 and 16. Theports 62 and 64 are formed to have their longer sides substantiallyparallel to the radial outermost tips of the lobes 38 and 30 of therespective main and gate rotors. In other words, the sides of the slots62 and 64 respectively form angles with the longitudinal axis of thechamber 56 which correspond substantially to the helix angles of therotors 26 and 28.

The compressor 10 includes a capacity control device characterized by arotatably turnable valve member 66 having a cylindrical plug portion 68closely fitend of the shaft 70 and, as may be seen from viewing FIG. 3,is meshed with a helical screw or worm gear 84 fastened to the end of acontrol shaft 86. The opposite 1 end of the control shaft 86 has a handwheel 88 connected thereto for manually turning the shaft and therotatable valvemember 66. As may be appreciated by those skilled in theart, suitable motorized actuating means may be used for turning thevalve member 66 in place of the manual operating means disclosed.

The valve member 66 is also characterized by a longitudinal passage 90extending from the end portion 74 through the shaft 70. A conduit 92 isconnected to the chamber 76 for conducting liquid to the passage 90inthe valve member 66. Referring to FIG. 6 also the cylindrical plugportion of the valve member 66 extends only partially around the shaft70 and is delimited by I a longitudinaledge 94. The cylindrical portion68 is. further delimited by a stepped helical control edge 96 which isoperable in response to turning the valve member 66, to sequentaillyopen and close the auxiliary ports 62 and 64. In this way, as is knownfrom US. Pat.

No. 3,088,658, the capacity or quantity of gas or working fluid passedthrough the compressor can be varied. The main portion of the helicaledge 96 isformed to be substantially parallel to the longitudinal sidesof the ports 62 for quick opening and closing of the ports in j responseto minimal rotational turning of the valve member. As the valve member66 is turned to progressively uncover the ports 62 from the inletend ofthe bores 14 and 16 toward the high pressure or discharge end delimitedby the end wall 20 the ports 64 are progressively opened also to provideadditional area for gas entrapped in the grooves 32 of the gate rotor tobe bypassed withminimum throttling losses back to the compressor inletport by way of the chamber 56 and passages 58 and 60. The arrangement ofauxiliary ports 62 and 64 and the configuration of the valve member 66provides for control of the capacity or gas throughput of the compressor10 from the maximum displacement provided by the rotors 26 and 28 tosubstantially zero flow.

A compressor of the type disclosed herein and operating with liquidinjected into the bores 14 and 16 has been found to have improvedefficiency over prior art nonliquid injected helical screw rotorcompressors with rotary type regulating valves. Such improvements areseen to be realized from a reduction in the clearance volume of theports 62 and 64 between the respective. y

bores 16 and 14 and the cylindrical plug portion 68 of the control valvemember 66. As may be seen in FIGS.

4 and 5, even though the cylindrical valve chamber 56 i is placed asclose to the rotor bores as is practical the j auxiliary ports 62 and 64occupy a finite volume or space in which compressed gas is trapped andreexpanded as the grooves of the rotors 26and 28 move progressively pastthe ports. By the use of liquid injected into the bores 14 and 16, theclearance volume of the ports 62 and 64 which are unopened issubstantially reduced because of a filling up of the ports with liquid.Therefore, as the rotors 26 and 28 compress gas in the chevron shapedchambers formed by the grooves and intermeshing lobes of the rotors, anegligible amount of gas is trapped in the ports 62 and 64 and lost toreexpansion as the lobe tips of the rotors pass over the ports.Moreover, with the improved liquid injection means associated with therotary capacity control valve of the present invention the efficiencyofliquid injected helical screw compressors is further improved.

The control valve member 66 of the present invention is furthercharacterized by a plurality of passages which extend radially withrespect to the longitudinal turning axis of the valve member from thelongitudinal passage 90 to the cylindrical surface of the plug portion68. The passages are spaced longitudinally along the valve member 66 andare also spaced apart in angular increments around the circumference ofthe cylindrical plug portion 68. FIGS. 7 through 10 illustrate planardevelopments of the cylindrical chamber 56 with a planar development ofthe cylindrical plug portion 68 of the control valve member 66superimposed on the chamber development to show various positions of thecontrol edge 96. The developments of FIGS. 7 through 10 also show pairsof liquid injection passages 100, 102, 104, a single passage 106, andfurther pairs of passages 108 and 110. All of these passages are incommunication with the longitudinal passage 90. The pairs of passages100, 102, 104, 108, and 110 are progressively smaller in diameter andeffective flow area, and accordingly provide for progressively smallerflow rates of liquid into the bores 14 and 16 as they respectivelycommunicate with the ports 64 on turning of the valve member 66. Thesingle passage 106 is smaller in diameter than the passages 104 butlarger than the passages 108. In the embodiment of FIGS. 1 through 10most of the liquid injection passages communicate only with the ports 64and some of the ports 62 are modified in shape to prevent unwantedregistration with the liquid injection passages.

FIG. 7 illustrates the maximum capacity position of the control valve 66wherein all of the ports 62 and 64 are closed. In this position onepassage 100 of the largest diameter is in communication with a port 64which assures that an adequate amount of liquid is injected into thebore 16 for cooling and sealing purposes. The location of liquidinjection shown by FIG. 7 is also into a chamber formed by the rotors 26and 28 which is only slightly reduced in volume but is no longer incommunication with the inlet port 48 as is true for all liquid injectionpositions in the embodiment of FIGS. 1 through 10. In this way theliquid injected into the compressor does not mix with the gas flowinginto the grooves 32 and 40 of the rotors until after a working chamberformed by the casing bores 14 and 16 and a pair of grooves of the rotors26 and 28 is no longer in communication with the inlet port 48. It isdesirable to avoid injecting liquid into the rotor grooves which arestill in communication with the inlet port in order to prevent unwantedreduction in filling of the grooves with inflowing gas. However, it isalso desirable to inject liquid at a position in the bores which willassure that liquid flows into all of the ports 62 and 64 which areunopened to thereby fill up the clearance space formed by the ports.

FIG. 8 illustrates a position of the valve member 66 in which two of theports 62 are open as well as one port 64. This position represents areduction in working fluid capacity of approximately 25 percent for thecompressor 10. Accordingly, portions of both of the smaller passages 102are in communication with a port 64 and are the only passages notblocked and in a no-flow condition by the close fit of the plug portion68 in the chamber 56. Since the compressor throughput capacity is nowreduced, a smaller quantity of liquid is required for adequate cooling.Moreover, excessive amounts of liquid cause unwanted pumping losses aswell as overcooling of the working fluid. Overcooling of the workingfluid can cause condensation of water vapor in air compressors workingin ambient atmosphere. Accordingly, with the control valve 66 of thepresent invention the rate of liquid injection and location of injectionwith respect to the rotor bores 14 and 16 is automatically controlled inaccordance with the rotary position of the valve member itself.

FIGS. 9 and 10 show further reduced capacity positions of the controlvalve member 66. In FIG. 9 the valve member is in a position in whichthe throughput capacity is reduced to approximately 50 percent of themaximum capacity of the compressor 10. One passage 104 is incommunication with a port 64 and the rate of liquid injection is furtherreduced from the rate of the positions of the valve member in FIGS. 7and 8. In FIG. 10, the control valve member 66 has been turned to openall of the ports 62 as well as all of ports 64 and the capacity of thecompressor has been reduced to substantially zero flow. One passage isin communication with a slot 112 in the casing which opens into the bore14 whereby a still further reduced quantity of liquid is injected intothe working chambers. In the zero capacity position of the valve member66 it is desirable to provide some lubrication for the intermeshedrotors and to cool working fluid which is disposed in the discharge port50 and the discharge passage downstream thereof and which is unavoidablyexpanded and recompressed by the intermeshing rotors 26 and 28. AlthoughFIGS. 7 through 10 illustrate four positions of the rotary control valvemember 66, including the maximum and zero capacity positions, it will beappreciated that the valve member may be turned to any position betweenthe limit positions for controlling the working fluid capacity of thecompressor 10. Moreover, as the valve member 66 is turned to reduce thecapacity of the compressor 10 the rate of liquid injection is alsoreduced as the injection passages are sequentially placed incommunication with the ports 64.

The arrangement of liquid injection passages in the control valve member66 is also advantageous for certain applications of the compressor 10wherein the discharge working pressure is increased and the compressorthroughput capacity is proportionally reduced to prevent overloading thecompressor driving motor. Referring to FIG. 2, the compressor 10 isshown in a system including a drive motor 114 which is drivablyconnected to the shaft 42 of the rotor 26. The compressor 10 alsoincludes an inlet filter 116 for filtering air admitted to thecompressor inlet opening 46. The compressor system of FIG. 2 alsoincludes a combination compressed air receiver and liquid separator andreservoir tank 118 having a liquid separator element 120 therein and afinal discharge conduit 122 for conducting liquid-free pressure air toits end use. A conduit 124 connects the discharge passage 54 of thecompressor 10 to the tank 118 for conducting the liquid-gas mixture fromthe compressor. A conduit 126 is connected to tank 118 for conductingliquid through a filter 128 and to a heat exchanger 130 from which theliquid is conducted back to the compressor through conduit 92. Theliquid is forced to recirculate back to the compressor 10 by thepressure differential which exists between the tank 118 and theparticular injection passage which is in communication with the workingchambers of the compressor.

In certain applications of the compressor system of FIG. 2, or a similarsystem, it may be desirable to increase the working pressure of thesystem including the pressure in the tank 118. Therefore, in order toavoid overloading the motor 114 the capacity of the compressor may berequired to be reduced to limit the power absorbed by the compressor towhat the motor can provide. This may be conveniently accomplished byadjusting the valve member 66 to reduce the compressor throughputcapacity by opening the required number of ports 62 and 64. Moreover, asthe valve member 66 is rotated to a new position, a progressivelysmaller diameter passage or pair of passages will become operable forinjecting liquid into the bore 16. Since the pressure differentialbetween the tank 118 and the point of liquid injection has beenincreased due to increasing the working pressure in the conduit 92 thesmaller diameter passages will limit the flow of liquid to a rate inaccordance with the needs of the compressor and will prevent excessiveamounts of liquid from being injected into the bore 16 through one ormore of the larger passages. In other words, for any position of thevalve member 66 the flow of injection liquid is automatically adjustedthanks to the arrangement and size of the passages 100, 102, 104, 106,108, and 110. If the capacity is reduced while working pressure is heldsubstantially constant the rate of liquid injection is reduced inaccordance with reduced gas throughput. If capacity is reduced andworking pressure is increased, the liquid injection rate normally willremain substantially constant thanks to the reduced size of theinjection passages operating at a higher pressure differential.Moreover, if it is desired to turn the valve member 66 to reduce thecapacity and the built-in volume ratio for operation of the compressorat low working pressures in order to conserve power absorption by thecompressor, then the rate of injection of liquid will be decreasedbecause the smaller liquid injection passages will be operable and atlower working pressures. This also will be'in accordance with the liquidinjection needs of the compressor for efficient operation.

A second embodiment of the present invention is illustrated in FIGS. 11through 15. Referring to FIGS. 11 and 12, a liquid injected helicalscrew rotor gas compressor is illustrated and generally designated bythe numeral 132. The compressor 132 includes a casing 134 having a pairof parallel intersecting bores 136 and 138 in which are disposedrespectively a pair of intermeshing helical screw rotors 140 and 142.The rotors 140 and 142 are of substantially the same configuration asthe rotors 26 and 28 of the compressor 10 and have, respectively,helical lobes 141 and 143 and intervening grooves 145 and 147.

The compressor 132 also includes a bearing support member 144 fastenedto the casing 134 and forming a high pressure end wall 146 of thecompressor working chambers formed within the bores 136 and 138. A discharge port 148 is formed in the end wall 146 for communicating thebores 136 and 138 with a discharge passage 150 for the compressorworking fluid. The compressor 132 also includes a bearing supportmember.

152 fastened to the casing 134 and forming a low pressure end wall 154.The member 152 further includes an inlet opening 156 and an inlet port158 for admitting working fluid such as air to the bores 136 and 138 forcompression and delivery to the discharge passage by the rotors 140 and142 in a known way. The inlet port 158 is basically of the axialconfiguration as opposed to the primarily radial inlet port of thecompressor 10. The members 144 and 152 include respective bearings 160and 162 for rotatably supporting the gate rotor 142. The main rotor 140is similarly supported by bearings, not shown, disposed in the members144 and 152. The main rotor 140 also includes an extendedshaft portion164 for drivably connecting the compressor.

132 to a suitable motive power means.

The casing 134 is provided with a cylindrical cham- I ber 166 formedclosely adjacent and parallel to the bores 136 and 138. The chamber 166has an open end The ports 178 are similar in configuration to theauxiliary ports 62 of the compressor 10. The casing 134 further includesa series of ports 180, as shown by the pla-.

nar development of FIG. 14, which open into the chamber 166 from thebore -138. A rotary capacity control valve member 182 is-provided in thecompressor 132 and is formed as a substantially cylindrical plug havinga radially inwardly relieved portion 184, FIG. 13, which is delimited bya helical control edge 186 and a longitudinal edge 188. The valve member182 is closely fitted in the chamber 166 and includes an axial passage190 which is in communication with a liquid inlet passage 192 formed inthe support member 152. A hub portion 194 on the valve member 182 isfitted in a recess in the i wall 172. A set screw 196 threaded into thewall172 is engaged with the hub 194 for locking the valve member 182 invarious rotative positions in accordance with the desired capacity ofthe compressor 132. As shown in FIG. 15, in which view the cover member174 is removed, a fiat sided socket 193 is provided in the end face ofthe hub 194 for insertion of a suitable wrench for turning the valvemember 182.

The valve member 182 is provided with a plurality of liquid injectionpassages designated by numerals 200,-

202, 204, 206, 208, 210 and 212 which are of progressively decreasingdiameter from the passage 200 to the passage 212. The passages 200through 212 are spaced axially along the valve member 182 and also aredis; posed spaced apart around the circumference of the cylindrical plugportion of the valve member. Each passage is in communication with thepassage 190 for conducting liquid to the bores 136 and 138 by way of theauxiliary ports 178 and 180. The passages 208, 212 and 210 are operableto be in registration with slots 216 and 214, FIG. 14, which open intothe bore 138. With the exception of passage 208 the passages 200 through212 are respectively in communication 'with elongated grooves of variouslengths and position on the cylindrical surface of the valve member 182.The arrangement of the passages 200 through 212 and their respectiveassociated grooves is such as to be cooperable withthe ports 178 and 180and the slots 214 and 216 to vary the amount and location of liquidinjected into the bores 136 and 138. This is in accordance with theposition of the control edge 186 and, accordingly, the capacity or gasthroughput of the compressor 132.

FIG. 14 illustrates a planar development of the cylindrical controlvalve member 182 superimposed on a planar development of the ports 178and 180. The development of the valve member 182 represented by thesolid lines shows the position of the valve with respect to the portswhen all ports are closed and the compressor is operating at the maximumdisplacement volume or capacity of the rotors 140 and 142. In thisposition the two largest diameter passages 200 and 202 are inregistration with the ports 180 and 178, respectively. The position ofthe valve 182 represented by the dashed lines is the maximum reducedcapacity position in which all ports 178 and 180 are open and incommunication with the chamber 166 and the inlet port 158. In thisposition the passages 210 and 212 of smallest diameter are inregistration with slots 214 and 216 for injecting a reduced quantity ofliquid in accordance with the reduced capacity or gas throughput of thecompressor 132.

As may be appreciated from the foregoing description and illustrationsof the compressor 132 the ports 178 and 180 do not extend toward thehigh pressure end of the casing 134 sufficiently to provide forreduction of compressor capacity to zero flow. The arrangement of thevalve member 182 is also provided for compressors wherein onlyinfrequent adjustment of capacity is required. Such a compressor as thecompressor 132 might be used where it would be required to operate thecompressor continuously at reduced capacity perhaps together withincreased inlet and/or discharge working pressures. In this way acompressor such as the compressor 132 could be operated continuously atreduced capacity more efficiently than by the use of certain othercapacity reduction means such as throttling the inlet gas flow. Inletthrottling could be used, however, for short term reduction of capacityto zero flow, if needed.

.What is claimed is:

1. In a helical screw gas compressor:

a casing having two parallel intersecting bores;

an inlet port and a discharge port opening into said bores;

interengaged helical screw rotors disposed in said bores andcharacterized by cooperating helical grooves and lobes forming workingchambers operable to entrap and compress gas admitted to said boresthrough said inlet port;

a cylindrical chamber formed in said casing and having an opening incommunication with said inlet port;

a plurality of auxiliary ports formed in said casing and opening to atleast one of said bores and to said chamber, said auxiliary ports beingspaced apart axially with respect to the longitudinal axis of said onebore;

a rotatably turnable control valve member disposed in said chambercharacterized by a portion forming a closure for said auxiliary portsdelimited by a control edge coactable with said auxiliary ports foropening and closing said auxiliary ports in response to turning saidvalve member whereby the gas throughput of said compressor is controlledin accordance with the opening and closing of said auxiliary ports bysaid valve member;

means for turning said valve member; and,

passage means for injecting liquid into said bores for mixing with saidgas being compressed by said rotors, said passage means being operablyassociated with said valve member whereby the effective fluid flow areaof said passage means is increased in response to the turning of saidvalve member to close said auxiliary ports.

2. The invention set forth in claim 1 wherein:

said passage means for injecting liquid into said bores is disposed insaid casing and is operable to control the axial position of liquidinjection with respect to the longitudinal axis of said bores inaccordance with the opening and closing of said auxiliary ports by saidvalve member.

3. The invention set forth in claim 2 wherein:

said passage means for injecting liquid into said bores is movablydisposed in said casing for injecting liquid into a working chamberformed by a pair of grooves of said rotors only after said workingchamber is no longer in communication with said inlet port.

4. The invention set forth in claim 2 wherein:

said valve member comprises a cylindrical plug portion closely fitted insaid chamber and delimited by said control edge, and said passage meanscomprises plural passages in said cylindrical plug portion operable tobe in communication with said auxiliary ports in accordance with therotative position of said valve member for injecting liquid into saidbores.

5. The invention set forth in claim 4 wherein:

said passages in said valve member are spaced apart axially with respectto the rotational axis of said valve member and said passages are spacedapart around and open to the circumference of said cylindrical plugportion whereby one or more of said passages are in communication withsaid auxiliary ports in accordance with the rotative position of saidvalve member.

6. The invention set forth in claim 4 wherein:

said compressor includes a conduit in communication with said dischargeport, a liquid separator and reservoir tank connected to said conduit,and conduit means connected to said reservoir tank and in communicationwith said passage means for conducting liquid to said passage means forinjection into said bores at a flow rate in accordance with thedifferential pressure between said reservoir tank and said auxiliaryport in communication with said passage means.

7. The invention set forth in claim 4 wherein:

said valve member includes a shaft portion and said means for turningsaid valve member includes a gear connected to said shaft portion, gearmeans meshed with said gear, and means for reversibly moving said gearmeans for causing the reversible rotation of said valve member.

8. The invention set forth in claim 4 together with:

means for locking said valve member in a predetermined rotativeposition, said means comprising a set screw disposed in said casing andengageable with said valve member.

9. In a helical screw gas compressor:

a casing having two parallel intersecting bores;

an inlet port and a discharge port opening into said bores;

interengaged helical screw rotors disposed in said bores andcharacterized by cooperating helical grooves and lobes forming workingchambers operable to entrap and compress gas admitted to said boresthrough said inlet port;

a cylindrical chamber formed in said casing and having passage means incommunication with said inlet port;

a plurality of auxiliary ports formed in said casing and opening to atleast one of said bores and to said chamber, said auxiliary portscomprising a series of oblique slots spaced apart axially with respectto the longitudinal axis of said one bore, the longer sides of saidslots forming an angle with respect to said longitudinal axis whichcorresponds substantially to the helix angle of the rotor disposed insaid one bore;

a rotatably turnable control valve member comprising a cylindrical plugportion closely fitted in said chamber and forming a closure for saidauxiliary ports delimited by a control edge coactable with saidauxiliary ports in response to turning of said valve member whereby thegas throughput of said compressor is controlled in accordance with theopening and closing of said auxiliary ports;

means for turning saidvalve member;

a longitudinal passage disposed in said valve member and incommunication with a source of liquid; and,

a series of radially extending passages in said valve member forinjecting liquid into said bores for mixing with the gas beingcompressed by said rotors and for filling up the clearance volume formedbetween said chamber and said one bore, said passages being spaced apartaxially toward said discharge port and with respect to the rotationalaxis of said valve member and connected to said longitudinal passage,said passages being spaced apart around and opening to the circumferenceof said cylindrical plug portion, and said passages including respectivegrooves formed on the circumference of said cylindrical plug portion andproportioned to be cooperable with said auxiliary ports to provideprogressively smaller effective fiow areas for injection liquid flowingto said bores in accordance with the turning of said valve member toprogressively reduce the gas throughput of said compressor, the amountof and axial position of injection of said liquid being in accordancewith the rotative position of said valve member. 10. In a helical screwgas compressor:

a casing having two parallel intersecting bores;

an inlet port and a discharge port opening into said bores; interengagedhelical screw rotors disposed in said bores and characterized bycooperating helical grooves and lobes forming working chambers ope -table to entrap and compress gas admitted to said bores through saidinlet port;

a cylindrical chamber formed in said casing and havl ing passage meansin communication with said inlet port;

a plurality of auxiliary ports formed in said casing and opening to atleast one of said bores and to said chamber, said auxiliary portscomprising a series of i oblique slots spaced apart axially with respectto the longitudinal axis of said one bore, the longer:

sides of said slots forming an angle with respect to said longitudinalaxis which corresponds substantially to the helix angle of the rotordisposed in said one bore; a rotatably turnable control valve membercompris ing a cylindrical plug portion closely fitted in said chamberand forming a closure for said auxiliary ports delimited by a controledge coactable with said auxiliary ports in response to turning of saidvalve member whereby the gas throughput of said compressor is controlledin accordance with the opening and closing of said auxiliary ports;means for turning said valve member; and,

a plurality of passages in said valve member spaced apart axially towardsaid discharge port and with respect to the rotational axis of saidvalve member, and having progressively smaller effective flow areastoward said discharge port, said passages,

being spaced apart around and opening to the circumference of saidcylindrical plug portion whereby one or more of said passages are incommunication with said auxiliary ports in accordance with the rotativeposition of said valve member for said passages are formed as pluralpairs of passages, each pair spaced axially closer to said dischargeport having a progressively smaller combined ef-' fective flow area.

1. In a helical screw gas compressor: a casing having two parallelintersecting bores; an inlet port and a discharge port opening into saidbores; interengaged helical screw rotors disposed in said bores andcharacterized by cooperating helical grooves and lobes forming workingchambers operable to entrap and compress gas admitted to said boresthrough said inlet port; a cylindrical chamber formed in said casing andhaving an opening in communication with said inlet port; a plurality ofauxiliary ports formed in said casing and opening to at least one ofsaid bores and to said chamber, said auxiliary ports being spaced apartaxially with respect to the longitudinal axis of said one bore; arotatably turnabLe control valve member disposed in said chambercharacterized by a portion forming a closure for said auxiliary portsdelimited by a control edge coactable with said auxiliary ports foropening and closing said auxiliary ports in response to turning saidvalve member whereby the gas throughput of said compressor is controlledin accordance with the opening and closing of said auxiliary ports bysaid valve member; means for turning said valve member; and, passagemeans for injecting liquid into said bores for mixing with said gasbeing compressed by said rotors, said passage means being operablyassociated with said valve member whereby the effective fluid flow areaof said passage means is increased in response to the turning of saidvalve member to close said auxiliary ports.
 2. The invention set forthin claim 1 wherein: said passage means for injecting liquid into saidbores is disposed in said casing and is operable to control the axialposition of liquid injection with respect to the longitudinal axis ofsaid bores in accordance with the opening and closing of said auxiliaryports by said valve member.
 3. The invention set forth in claim 2wherein: said passage means for injecting liquid into said bores ismovably disposed in said casing for injecting liquid into a workingchamber formed by a pair of grooves of said rotors only after saidworking chamber is no longer in communication with said inlet port. 4.The invention set forth in claim 2 wherein: said valve member comprisesa cylindrical plug portion closely fitted in said chamber and delimitedby said control edge, and said passage means comprises plural passagesin said cylindrical plug portion operable to be in communication withsaid auxiliary ports in accordance with the rotative position of saidvalve member for injecting liquid into said bores.
 5. The invention setforth in claim 4 wherein: said passages in said valve member are spacedapart axially with respect to the rotational axis of said valve memberand said passages are spaced apart around and open to the circumferenceof said cylindrical plug portion whereby one or more of said passagesare in communication with said auxiliary ports in accordance with therotative position of said valve member.
 6. The invention set forth inclaim 4 wherein: said compressor includes a conduit in communicationwith said discharge port, a liquid separator and reservoir tankconnected to said conduit, and conduit means connected to said reservoirtank and in communication with said passage means for conducting liquidto said passage means for injection into said bores at a flow rate inaccordance with the differential pressure between said reservoir tankand said auxiliary port in communication with said passage means.
 7. Theinvention set forth in claim 4 wherein: said valve member includes ashaft portion and said means for turning said valve member includes agear connected to said shaft portion, gear means meshed with said gear,and means for reversibly moving said gear means for causing thereversible rotation of said valve member.
 8. The invention set forth inclaim 4 together with: means for locking said valve member in apredetermined rotative position, said means comprising a set screwdisposed in said casing and engageable with said valve member.
 9. In ahelical screw gas compressor: a casing having two parallel intersectingbores; an inlet port and a discharge port opening into said bores;interengaged helical screw rotors disposed in said bores andcharacterized by cooperating helical grooves and lobes forming workingchambers operable to entrap and compress gas admitted to said boresthrough said inlet port; a cylindrical chamber formed in said casing andhaving passage means in communication with said inlet port; a pluralityof auxiliary ports formed in said casing and opening to at least one ofsaid bores and to said chamber, said auxiliary ports comprising a serIesof oblique slots spaced apart axially with respect to the longitudinalaxis of said one bore, the longer sides of said slots forming an anglewith respect to said longitudinal axis which corresponds substantiallyto the helix angle of the rotor disposed in said one bore; a rotatablyturnable control valve member comprising a cylindrical plug portionclosely fitted in said chamber and forming a closure for said auxiliaryports delimited by a control edge coactable with said auxiliary ports inresponse to turning of said valve member whereby the gas throughput ofsaid compressor is controlled in accordance with the opening and closingof said auxiliary ports; means for turning said valve member; alongitudinal passage disposed in said valve member and in communicationwith a source of liquid; and, a series of radially extending passages insaid valve member for injecting liquid into said bores for mixing withthe gas being compressed by said rotors and for filling up the clearancevolume formed between said chamber and said one bore, said passagesbeing spaced apart axially toward said discharge port and with respectto the rotational axis of said valve member and connected to saidlongitudinal passage, said passages being spaced apart around andopening to the circumference of said cylindrical plug portion, and saidpassages including respective grooves formed on the circumference ofsaid cylindrical plug portion and proportioned to be cooperable withsaid auxiliary ports to provide progressively smaller effective flowareas for injection liquid flowing to said bores in accordance with theturning of said valve member to progressively reduce the gas throughputof said compressor, the amount of and axial position of injection ofsaid liquid being in accordance with the rotative position of said valvemember.
 10. In a helical screw gas compressor: a casing having twoparallel intersecting bores; an inlet port and a discharge port openinginto said bores; interengaged helical screw rotors disposed in saidbores and characterized by cooperating helical grooves and lobes formingworking chambers operable to entrap and compress gas admitted to saidbores through said inlet port; a cylindrical chamber formed in saidcasing and having passage means in communication with said inlet port; aplurality of auxiliary ports formed in said casing and opening to atleast one of said bores and to said chamber, said auxiliary portscomprising a series of oblique slots spaced apart axially with respectto the longitudinal axis of said one bore, the longer sides of saidslots forming an angle with respect to said longitudinal axis whichcorresponds substantially to the helix angle of the rotor disposed insaid one bore; a rotatably turnable control valve member comprising acylindrical plug portion closely fitted in said chamber and forming aclosure for said auxiliary ports delimited by a control edge coactablewith said auxiliary ports in response to turning of said valve memberwhereby the gas throughput of said compressor is controlled inaccordance with the opening and closing of said auxiliary ports; meansfor turning said valve member; and, a plurality of passages in saidvalve member spaced apart axially toward said discharge port and withrespect to the rotational axis of said valve member and havingprogressively smaller effective flow areas toward said discharge port,said passages being spaced apart around and opening to the circumferenceof said cylindrical plug portion whereby one or more of said passagesare in communication with said auxiliary ports in accordance with therotative position of said valve member for injecting liquid into saidbores for mixing with the gas being compressed by said rotors and forfilling up the clearance volume formed by said auxiliary ports betweensaid chamber and said one bore, the amount of and axial position ofinjection of said liquid being in accordance with the rotative positioNof said valve member.
 11. The invention set forth in claim 10 wherein:said passages are formed as plural pairs of passages, each pair spacedaxially closer to said discharge port having a progressively smallercombined effective flow area.